Avalanche Forecast

Archived

Feb 8th, 2013–Feb 9th, 2013

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

South Coast.

Confidence

Good

Weather Forecast

Saturday: A ridge of high pressure builds and settles in. Expect mostly sunny skies, light northerly winds and alpine temperatures around -1.Sunday & Monday: The ridge continues to dominate. Expect continued sunny skies, light northerlies and high freezing levels each afternoon.

Avalanche Summary

Natural activity up to size 2.5 has been observed on north through east aspects where the recent storm snow is 25cm or deeper. These events have been predominantly failing in the alpine and upper treeline, with one, anomalous event at a lower elevation (1500m). A brief sunny period on Feb 7 saw moist, solar triggered sluffing below treeline in the Coquihalla area. Isolated, small rider triggered avalanches have also been reported.

Snowpack Summary

The dribs and drabs of new snow has ended. Around 30-40cm fell on average, with more (up to 65cm) in the Coquihalla area. Consistent southwesterly winds during the storm period has redistributed the new snow into fresh windslabs on lee terrain features in the alpine and at treeline. The newly buried surfaces (Feb.3 interface) are old wind slabs (behind ridges, ribs and on lee slopes) and sun crusts on south and west facing slopes. In isolated locations, this interface is small surface hoar. Down a further 20-50 cm sits a persistent interface comprising of crusts, facets and/or surface hoar crystals. Recently, this layer has been reactive only in sheltered areas at and below treeline where the surface hoar lingers. Tests on this layer have shown vastly different results, from a partial block RB6 to a moderate, sudden extended column test with a positive propensity for propagation. This really highlights the variability of the layer and the need to dig down to find and test the layer before committing to steep terrain. The mid and lower snowpack is generally well settled and strong.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.